var img_swiper = document.querySelector("#img_swiper"),
  img_btn = document.querySelectorAll(".img_btn"),
  ol = document.querySelectorAll("#point li");

img_btn.forEach(function (val, index) {
  val.addEventListener('click', function () {
    var i = index + 1;
    img_swiper.src = 'img/article_0' + i + '.jpg';
    var j = index > 3 ? index - 4 : index;
    ol.forEach(function(val){
      val.classList.remove('active');
    })
    ol[j].classList.add('active');
  })
})
